Color-kinescopes, etc.



Oct. 5, 1954 H. s. ALLWINE 2,691,116

COLOR-KINESCOPES ETC Filed March 31, 1953 Ffg.

IN I E NTOR.

UWM

Patented Oct. 5, 1954 COLOR-KINESCOPES, ETC.

Harrison S. Allwine, Trenton, N. J., assigner to Radio Corporation of America, a corporation of Delaware Application March 31, 1953, Serial No. 345,891

11 Claims.

This invention relates to color-kinescopes, camera tubes and other (e. g. stereoscopic) cathode-ray devices of the kind containing a screen-unit or target assembly made up of one or more parallel-wire grills through which beam-electrons pass in their transit to a nearby screen.

The principal object of the invention is to reduce wire vibration and thus to reduce colordilution, loss-of-contrast and other image-defects resulting from grill-wire vibration.

The problem of grill-wire vibration in CR tubes of the general character described has long been recognized and several ways of solving it have heretofore been proposed. By way of example; Dr. Flechsig in his 1941 French Patent 866,065 discloses a color line-screen unit including a grill comprising a series of parallel metal wires whose spacing is maintained by several very ne wires positioned at right angles to the first wires. One very real objection to re-inforcing wires (however thin they may be) is that their shadow mars the image sketched on the screen by the moving pencil of electrons. Another proffered solution of the problem involves the use of relatively thick and strong reinforcing rods or damping bars and a number of auxiliary electronlens elements for re-umting the beam after it is split by said rods or bars. Still another proposal involves the use oi a multiplicity of springlike supports for damping the vibration .of each length of wire. irrespective of the efficacy of such proposals it may be said that they are far more complicated and expensive than is desirable in a home instrument, or one which should be produced by mass-production methods.

Accordingly, another and important object of the present invention is to provide a vibrationfree color-kinescope which, by reason of the simplicity and economy of its parts, lends itself readily to mass-production methods.

Stated generally, the foregoing and related objects are achieved in accordance with the invention by constructing the grill (or grills) of high tensile strength wire having an effective resistance many times lower than that exhibited by the taut wire grills of the prior art. The lower effective resistance of the grill wire lowers the voltage excitation caused by scanning and this in turn reduces the tendency of the wire to vibrate. Optimum freedom from vibration is achieved when the screen and other elements, if any, ofthe target assembly, to which the grill is capacitively coupled, also exhibit a very lowvalue of resistance. The high tensile strength and low resistance of the grill, required by the invention, may be achieved either (a) by plating a wire having the requisite high tensile strength with a metal of low electrical resistance or (b) by using Va twisted cable in which some of the strands are of high tensile strength material and the other or others consist, essentially, of copper or similar (e. g., silver or aluminum) substance of low electrical resistance.

The invention is further described in connection with the accompanying single sheet of drawings, wherein:

Fig. 1 is a partly diagrammatic view in per spective of a S-gun, single-grill color-kinescope embodying the invention;

Fig. 2 is a fragmentary view on an enlarged scale of a part of the grill-wire and frame of the screen-unit of Fig. 1;

Fig. 3 is an end view of a multi-strand cable whichmay be used in place of the plated wire of Fig. 2;

Fig. 4 shows the invention applied to a colortube of the so-called post-deected variety having a bi-part co-planar beam-deflecting grill, similar to the one shown in Schroeder 2,446,791;

Fig. 5 is a longitudinal sectional view of the viewing chamber of a color-kinescope containing a screen-unit including two plated wire grills arranged with their wires in register with each other to form the elements of a compound cylindrical lens; and

Fig. 6 is a view in perspective of a line-screen unit having two plated-wire grills arranged with the wires of onegrill parallel to the color-lines and the wires of the other grill at right angles to the first grill, as taught by Edward G. Ramberg in copending application Serial No. 277,182.

Whena wire grill is scanned in conventional television raster fashion, some of the beam current is intercepted by the grill Wires and flows through them to the frame, causing a voltage drop because of the resistance of the wires. When, as is usually the case, the grill is mounted close to another eld electrode (such as a metalized phosphor screen or another grill) there is an electrostatic force on each wire tending to bow it toward the other electrode. When the voltage on either is changed, the force cn the wire changes also, being proportional to the square of the voltage diierence existing between the wire and the other electrode.

Because of the nature of the scanning process, the current in any given wire is in the form of pulses, and normally contains components that 3 correspond to the horizontal and vertical scanning frequencies and their harmonics.

The resistance through which the beam current ows, while in the Wire, is constantly changing, also, being a maximum when the beam strikes the middle of the wire, and practically zero when it strikes the end. This, together with the pulsed nature of the current, causes the voltage change to have strong components in the two scan-frequencies and their harmonics.

In addition, the point of impact, and therefore the point of maximum voltage change, is, for part of the time, near the middle of the wire, where a change in force has the maximum ability to cause fundamental frequency vibrations, and at other times near the end, where this ability approaches zero.

Because the tension may differ slightly from wire to wire, and differs in the same wire from time to time as changes in picture brightness cause changes in the wire temperature, the fundamental frequencies of vibration extend over a large range. It is inevitable, therefore, that at some time the resonant frequency of one or more wires will coincide with some harmonic of a scan frequency (generally of the vertical scan frequency).

When this happens, the tendency of the wire to vibrate is greatly increased and, if there is also some slackening of the wire due to heating from electron bombardment, the amplitude of vibration can readily cause enough shift in the shape or position of the cylindrical electrostatic lens to cause electrons to strike the wrong color phosphor strip.

When very thin wires are used, to allow high transmission and consequently bright pictures, the effect is aggravated because the thinner wires have higher resistance, causing the excitation to be increased. Also, having less mass, a given excitation can cause vibrations of greater amplitude.

Enlarging the screen-unit also adds to the difficulty, because the longer wires have more resistance, and also vibrate with greater amplitude for a given value of voltage swing.

In large tubes, wire having a tensile strength not less than that of Nichrome is usually required to reduce to a minimum the sag of the wires under the steady force of a strong field. But wires of such high tensile strength are, unfortunately, relatively poor conductors and their use aggravates the vibration problem by causing greater voltage swings when the grill is scanned.

In accordance with the present invention a very substantial reduction in the exciting force is obtained by the use of a relatively thin plating of a good conductor, such as copper or silver, on the wires. In this manner, a stainless steel wire 0.003 in diameter and 18l long, with a resistance of about 150 ohms, can easily have its resistance reduced by a factorof 10, by a plating of copper which brings its diameter up to about 0.0035". This reduces the excitation by a similar factor and so minimizes the possibility of vibration.

Fig. 1 shows the invention as applied to a colorkinescope of the so-called Zi-gun, line-screen variety, iirst disclosed by Dr. Elechsig in French patent 866,065 of 1941, (and its German equivalent, No. 736,575 of 1943). Here the screenunit comprises a transparent screen plate 3 marked on its rear or target surface with a multiplicity of groups of lines R, B and G arranged in a repetitive pattern and constituted of phosphor materials of different color-response characteristics, such, for example, as red (R), blue (B) and green (G) respectively. The phosphor surface of the screen is covered all over with an electron-transparent electrically continuous conductive coating 5 constituted, for example, of evaporated aluminum at least one thousand angstrom units thick.

The grill with which the present invention is especially concerned, is mounted closely adjacent to the conductive target surface 5 of the colorscreen. It comprises a metal frame l and, conveniently, a single-wire 9 (see Fig. 2) wound back-and-forth tautly, on pins l l-I l parallel to the phosphor-lines R, B and G on the screenplate, there being one grill aperture (i. e., two adjacent lengths of wire) for each group (R, B and G) of phosphor lines. The wire, or each cross-piece thereof, is very tightly stretched on the frame 'l and, to this end, should be formed at least in part of a metal of great tensile strength such, for example, as Nichrome (nickel chromium 20%), stainless steel, steel, tungsten or the like. In order to achieve the low value of electrical resistance necessary to the practice of the invention the wire 9 may be provided with a coating i3 of copper or of silver or other' highly conductive metal, as shown in Fig. 2, or it may be constructed in the form of a twisted cable, Fig. 3, made up of a number of strands some of which are constituted of steel or the like and at least one strand VI of copper or similar (low resistance) metal.

As taught in the Flechsig foreign patents, the screen 5 and its grill 9 may be operated either at the same potential or with the screen at a potential higher than that of the grill. In the latter case, here illustrated, electrons passing between the parallel wires are subjected to the focusing action of a cylindrical electron-lens eld which is set up in the grill-screen space by reason of the diiference in potential between said parts of the screen-unit. In the instant case the red, blue and green electron-guns (r, b and y, respectively) are arranged delta-fashion with common horizontal and vertical deflection coils i9 and 2i, as taught in U. S. Patent 2,595,548 to Alfred C. Schroeder.

Figs. 4, 5 and 6 are included to show that the invention is not limited in its useful application to the single grill tubes of the Flechsig type, but may be applied to cathode-ray tubes of other varieties, including various types of plural-grill tubes.

The color-screen unit shown in Fig. 4 is of the "switching-at-the-screen variety described in U. S. Patent 2,446,791 to Alfred C. Schroeder. Here the grill is made up of alternate and intermediate sets of wires 23 and 25, respectively, to which color-switching voltages may be applied as by a square-wave (or sine-wave) generator 2l. As described in the Schroeder patent the grills are co-planar and the color phosphor lines on the screen are in a sequence such as R G R B R G R (instead of R B G R B G). Here both parts of the bi-part grill will be understood to be constructed, in accordance with the present invention, of composite wire, either of the plated type shown in Fig. 2 or the twisted cable type shown in Fig. 3. As in the Flechsg patents, the conductive screen plate 29 is maintained at a potential higher than that of the grill in order to establish a cylindrical lens-field in the grillscreen space.

Fig. 5 shows a color-screen unit similar to the one shown in Fig. 1 but having two parallel-wire grills 3i and 33 spaced apart in parallel planes with the wires in exact register with each other and connected to points of successively higher voltages on a voltage divider 35 to provide a compound cylindrical lens field. Here the number of wires in each of the grills 3l and 33 corresponds substantially to the number of groups of red (R) blue (B) and green (G) phosphor lines on the metalized screen 31. As shown in the drawing the screen 31 is maintained at a potential higher than that of either of the two compositewire grills 3l and 33.

Fig. 6 shows the invention applied to a colorscreen unit of the post decelerated type described by Edward G. Ramberg in co-pending application Serial N o. 277,182. Here, two parallele wire grills lll and 43 are arranged at right angles to one another with the composite wires of one grill (in this case, grill 13) parallel to the phosphor lines R, B and G on the metalized screen 45. The grill (43) that lies next adjacent to the screen 45 has a voltage applied thereto which is equal to or greater than the voltage applied to the screen. As a consequence, there is no retarding eld adjacent to the screen. Similarly, there is no field capable of accelerating low-velocity secondary-electrons (emitted by impact of beam-electrons upon the grills ll and 43) toward the screen. Thus, the only parts of the screen that are activated at any given momentA are those phosphor lines that lie directly in the path of the scanning beam or beams.

From the foregoing description it should now be apparent that the present invention provides an effective means for minimizing wire-vibration and consequent color-dilution, loss of contrast and other image-defects in cathode-ray tubes of the kind containing one or more parallel-wire grills through which beam-electrons pass in their transit to a nearby screen.

What is claimed is:

1. A cathode-ray tube comprising, an electrongun, a screen-unit including a conductive element and a taut iine-wire grill mounted in closely spaced relation in a position to be scanned by an electron-beam from said gun whereby at least a part of said grill tends to vibrate when sub- `iected to a Varying potential resulting from the iiow of beam-current through the electrical resistance of the ne-wire of which said grill is comprised, and a body of highly conductive metal contiguous said fine-wire throughout its length to reduce the effective resistance of said wire to the flow of said beam-current and thus to reduce said tendency of said grill to vibrate.

2. 'I'he invention as set forth in claim 1 wherein said grill wire comprises a core portion of high tensile-strength and said body of highly conductive metal surrounds said core.

3. The invention as set forth in claim 1 wherein said grill wire comprises a multi-strand cable and said body of highly conductive metal comprises at least one of the strands of said cable.

CII

4. The invention as set forth in claim 1 and wherein the conductive element with which said grill is closely associated comprises the target surface of a ray-sensitive screen-electrode.

5. The invention as set forth in claim 1 and wherein the conductive element with which said grill is closely associated comprises a second iinewire grill.

6. A cathode-ray tube comprising; an electrongun, a screen unit including a conductive element and a taut fine-wire grill mounted in closelyspaced relation in a position to be scanned by an electron-beam from said source, said grill wire comprising a core portion constituted of a material having a tensile strength substantially no less than that of Nichrome and a second por; tion in intimate contact with said core and constituted of a material that exhibits electrical resistance of a small fraction of the resistance of said core material.

7. The invention as set forth in claim 6 and wherein said second portion of said grill wire comprises an outer coating of copper on said core.

8. A cathode-ray tube comprising; an electrongun, a screen-unit including first and second taut fine-wire grills mounted in capacitive relation in a position to be scanned by an electron-beam from said gun whereby at least a part of one of said grills tends to vibrate when subjected to a Varying potential resulting from the flow of beam current through the electrical resistance of the fine-wire of which said grills are comprised, and a coating of highly conductive metal on said wire to minimize said tendency to vibrate.

9. The invention as set forth in claim 8 and wherein said first and said second coated fine-wire grills are mounted in a common plane.

10. The invention as set forth in claim 8 and wherein said rst and second coated fine-wire grills are mounted in spaced-apart parallel planes.

11. The invention as set forth in claim 8 and wherein the wire of said second grill extends at right angles to the Wire of said rst grill.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date Re. 23,672 Okolicsanyi June 23, 1953 1,722,121 Wilson July 23, 1929 1,989,954 Van Gessel Feb. 5, 1935 2,040,173 Gustin May 12, 1936 2,416,056 Kallmann Feb. 18, 1947 2,446,791 Schroeder Aug. 10, 1948 2,472,760 Ratchford June 7, 1949 2,539,096 Miner Jan. 23, 1951 2,556,864 Apker June 12, 1951 2,595,548 Schroeder May 6, 1952 2,625,666 Williams Jan. 13, 1953 2,653,263 Lawrence Sept. 22, 1953 FOREIGN PATENTS Number Country Date 866,065 France Mar. 31, 1941 

